1. Field of the Invention
The present invention relates to a load control device for controlling the amount of power delivered to an electrical load, specifically, to an electronic dimming ballast for a gas discharge lamp that is able to measure a number of operating characteristics, and to determine that a fault condition in the lamp in response to the measured operating characteristic.
2. Description of the Related Art
A load control device is operable to control the amount of power delivered from an alternating-current (AC) power source to an electrical load, such as a lighting load or a motor load. Typical load control devices include, for example, dimmer switches for lighting loads, electronic ballasts for gas discharge lamps, light-emitting diode (LED) drivers for LED light sources, and motor control devices for motor loads. Some prior art load control device have included power measurement circuits for measuring an input current of the load control device. For example, the power measurement circuit may comprise a current transformer coupled in series with a hot terminal of the load control device for sensing the input current as described in greater detail in commonly-assigned U.S. Pat. No. 6,528,957, issued Mar. 4, 2003, entitled POWER/ENERGY MANAGEMENT CONTROL SYSTEM, the entire disclosure of which is hereby incorporated by reference. Since current transformers tend to be large and expensive, some prior art lighting control devices have estimated the magnitude of the input current in dependence upon the present intensity of the controlled lighting load as described in commonly-assigned U.S. patent application Ser. No. 12/550,972, filed Aug. 31, 2009, entitled METHOD OF LOAD SHEDDING TO REDUCE THE TOTAL POWER CONSUMPTION OF A LOAD CONTROL SYSTEM, the entire disclosure of which is hereby incorporated by reference.
However, there is a need for a load control device that is more accurately able to measure operating characteristics (such as input power) without requiring a current transformer.